The present invention is generally related to a communication cable and, more particularly, is related to a fiber optic cable structure for installation using blowing techniques and a method for installation.
Fiber optic cables have been used for years to transmit information at high rates and very long distances. In a typical fiber optical cable, information is transmitted through a hair-thin optical fiber, usually composed of glass. The glass optical fiber is not typically ductile, and may be easily broken, chipped, and cracked. Such damage to the optical fiber can degrade or attenuate the signal being transmitted. Therefore, optical fibers are housed in cable structures to protect the fibers from damage, such as damage caused by heavy loads; sharp impacts; environmental stresses, including temperature change (especially in indoor/outdoor applications); etc.
For example, environmental temperature variations during product life of the fiber optic cable can cause the typical plastic used as the outer layer of fiber optic cable structures to expand and contract, applying tensile and axial compressive loads on the cable structure, including the glass optical fibers. Similarly, a significant instance of contraction by the plastic can occur during manufacture of the cable itself
There are several relatively common cable structures currently being used to protect these hair-thin optical fibers. Such cable structures include the loose tube, the slotted core and the central core structures. In loose tube fiber optic cables, the glass fibers lie in buffer tubes, which are generally filled with some sort of water blocking compound. The loose tube buffer tubes are typically arranged around a central strength member or core and a plastic material is extruded over the buffer tubes and core as the final layer of the cable structure, usually in a continuous, high-speed sheathing operation.
In a slotted core cable, the glass optical fibers are housed in channels or slots that are typically filled with a water blocking material such as a gel. The channels or slots are symmetrically arranged around a central strength member or core, and form helical (or reverse-helical) grooves extending along the longitudinal axis of the cable for receiving one or more glass optical fibers. As with the loose tube configuration, the final layer of a cable structure typically is an extruded plastic jacketing material.
In a monotube cable, the glass fibers are typically housed in a central tube, which is generally filled with some type of water blocking compound. Instead of being centrally located, the strength elements in a monotube cable are arranged linearly along or helically about the central tube. The final layer of the cable structure typically is an extruded plastic jacketing material.
Design and implementation of fiber optic cable structures attempt to balance the need for protection of the thin glass optical fibers against the need for cost effective, easily installed cable structures. Thicker, more rigid cables provide better protection of the fibers, but are difficult to manage and costly to install.
Flexible, easily installed cable structures typically provide less protection to the glass fibers, especially when the cables are to be installed into conduits (such as when installing new fiber optic lines in urban areas). Such installations previously involved pulling the cables through the conduit. Pulling the cable places tensile loads on both the cable structures and glass fibers that can easily damage the fibers, especially in long runs of cable.
Techniques have been developed to use compressed air to blow fiber optic cables into conduits. These techniques typically use compressed air to surround the fiber optic cable in the conduit, buffering the cable from the conduit, and allowing the cable to be installed with much less tensile or compression load being placed on the cable. Additionally, some techniques use the drag created by the compressed air flowing over the surface of the cable to move the fiber optic cable through the conduit.
However, these blowing techniques are typically hampered by the rigidity of typical fiber optic cables, and the surface friction between the cable structure and the conduit. Current cable structures including epoxy and Polybutylene Terephthalate (PBT) structures only address one or the other of the impediments to blowing, and are not cost effective.
Accordingly, there does not exist a fiber optic cable structure that is sufficiently flexible and low in surface friction to allow easy installation of the cable structure in conduits through a blowing technique, while at the same time providing sufficient protection to the glass optical fibers carrying the signals.
Thus, a heretofore-unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
The foregoing problems have been overcome by an optical fiber cable structure including a tube comprised of inorganic fillers dispersed within a soft resin, the tube housing optic fibers or ribbons surrounded by a water blocking material. The use of the inorganic fillers in the soft resin will provide a cable structure with superior blowing performance due to low surface friction and high flexibility, allowing more effective installation of the fiber optic cable via blowing techniques.
The use of the inorganic fillers in the soft resin reduces the thermal expansion/contraction of the cable structure, resulting in improved optical performance at temperature extremes encountered in the Outside Plant environment. The use of the inorganic fillers in the soft resin also improves processing stability during cable fabrication, and increases the robustness of the cable structure, including the compression resistance of the cable structure to axial loads, providing protection to the optical fibers.
Possible examples of the type of resins that may be incorporated into the cable structure include: polyethylenes; impact-modified polypropylene; polypropylene-based thermoplastic olefins; ethylene-vinyl acetate resins; plasticized poly(vinyl chloride); polyester-based thermoplastic elastomers; and polyether-based thermoplastic elastomers or any other base resin with an elastic (Young""s) modulus of 200,000 psi or less at 25xc2x0 C.
The fillers may be either fibrous, platelike, or round in nature and possible fillers include: talc; wollastonite; mica; montmorillionite; bentonite; kaolinite clay; smectite clays; synthetic clays; fumed silica; fumed alumina; glass beads; glass flake; glass fiber; aluminum trihydrate; and magnesium hydroxide.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention.